THE AMERICAN LOBSTER. 227 



In the treatment of these eggs I have profited by the experience and advice of 

 my friend Dr. William. Patten, whose method of mounting the ova of Arthropods, 1 and 

 orienting them for the microtome, which I have essentially followed, leaves little to be 

 desired. A cell is made of strips of cardboard of the desired thickness, and the 

 respective hemispheres of each egg are fixed in place by a small drop of concentrated 

 Schallibaum's fixative. The cell may be flooded with turpentine while tlie process of 

 fixation is going ou, and when drained thick balsam is added and the cover glass is 

 afterwards applied. In this way the most perfect and beautiful preparations can be 

 made. 



Eggs are hardened in the same way, when the object is to cut them into sections. 

 They may be successfully embedded in either paraffin or celloidin. Bumpus has 

 described his successful use of the latter reagent, which he heartily recommends. 2 

 This method is undoubtedly the surest although the most laborious to pursue. I have 

 obtained excellent sections of the early and late stages of development by the paraffin 

 method, and for the older embryos it is certainly preferable. Turpentine and all the 

 essential oils soon harden the yolk so that it firmly resists the knife. The eggs should 

 therefore be allowed to remain in the clearing fluid for the shortest possible time ouly, 

 and then thoroughly saturated with paraffin. The method which Patten has given 

 for orientation can hardly fail to meet with success. 



Appendix II.— COMPOSITION OF THE SHELL AND GASTROLITHS OF THE 



LOBSTER. 



[By Albert W. Smith, Ph. D., Associate Professor of Chemistry in the Case School of 'Applied Science.'] 



The analyses of the shell of the lobster were made from four distinct individuals, 

 taken at Woods Hole, Massachusetts (Xos. 1 to 4 in the table below), and were selected 

 with reference to the molting period. The description of the shells and lobsters from 

 which they were taken is as follows : 



No. 1. Hard-shell female with external eggs, August 3, 1894. 



No. 2. A hard-shell female lobster near the point of egg-laying; length, 11 inches; July 16, 1894. The 



ovarian eggs of this lobster were mostly absorbed. (See p. 48.) 

 No. 3. From a female near the point of molting; length, 10 inches; August 2, 1894. (The gastroliths 



of this "shedder" are described on p. 89, and their chemical analysis is given in No. 3a of 



the following table.) 

 No. 4. The molted shell of a male 11 inches long. (See No. 2, table 24, and p. 89.) 



The gastroliths subjected to analysis have the following history: 



No. Qa is taken fresh from the gastrolithic sac of a "shedder." (For drawing of this gastrolith sepa- 

 rated into its constituent spicules see fig. 165, plate 42.) 



No. 3a is from lobster No. 3 of this table, taken fresh from the gastrolithic sac of the animal shortly 

 before it was ready to molt. 



No. 4a is from the lobster which cast off shell No. 4 of this table, taken from the stomach of the animal 

 when soft and preserved in alcohol. (For drawings of this gastrolith see cut 8, plate C; for 

 description of lobster No. 2, table 24.) 



1 Orienting Small Objects for Sectioning, and " Fixing " them, when Mounted in Cells. (Ameri- 

 can Naturalist, vol. 28, pp. 360-362, 1894. ) 



2 American Naturalist, vol. 26, pp. 80-81, 1892. 



